This invention relates to semiconductor surface measurement and in particular to a method suitable for measuring the interface trap density (interface state density) at the interface between semiconductor and insulator, the quantity and the distribution of electric charge in the insulator, the life time of carriers in the semiconductor, etc. and an apparatus for realizing the same.
As a representative prior art method of semiconductor surface measurement there is known a method, by which capacitance-voltage (C-V) characteristics are obtained. For the C-V measurement the high frequency (1 MHz) method, the low frequency method, the quasistatic method, etc. are used. The C-V characteristics can be obtained usually by forming an insulating layer 2 on a semiconductor substrate 1 and forming further an electrode 3 made of metal, polycrystalline silicon, etc. Thereon by the evaporation or the chemical vapor deposition (CVD) method as indicated in FIG. 2, so as to obtain a so-called MOS (metal-oxide-semiconductor) structure. A C-V measuring apparatus incorporates a power supply for applying a DC bias thereto.
As a simple method, the C-V characteristics can be measured by putting a drop of mercury or indium-gallium alloy 3a on the insulator 2 formed on the semiconductor substrate 1 so as to obtain an MOS structure, which drop is thrust against the insulator by means of a conductive (metal) rod 5, and using a C-V measuring apparatus 20, as indicated in FIG. 3.
As another method of semiconductor surface measurement, there is known a method of surface photo voltage measurement disclosed in Japanese Journal of Applied Physics, 23 (1984) pp. 1451-1461. The principle of this method is indicated in FIG. 4. That is, a transparent insulator 6 such as Mylar is inserted as a spacer between a transparent electrode 3b supported by a glass plate 7 and the insulator 2 formed on the semiconductor substrate 1 and the insulator 2 is irradiated with light 22 emitted by a light source 21 driven by an AC power supply through an optical system 23. A signal synchronized with the irradiation with the light 22 is inputted in an AC surface photo electro-motive force measuring apparatus 24 and the surface photo electro-motive force measurement is effected through a capacitance. The SPM (Surface Photon Microscope) using the surface photo voltage is described by Chuske MUNAKATA in Oyo Butsuri Vol. 53, No. 3 (1984) pp. 176-182.